[vSphere] Support datacenters that are located below folders not in root...

## Background ##
In big vmware installations datacenters might be organized in subfolders.
Normally the vmware datacenters are located in the "root" folder of vmware but when having loads of dcs it is a common approach to organize the dcs in different folders.

Right now fog cannot cope with this problem.

If a datacenter is located in different folders no guests can be queried or selected as the referring datacenter cannot be found.

## Solution ##

This solution add a path to each datacenter that points to the location of the dc.
The path is an array of parent locations of the dc and will be recursively evaluated when searched for the dc name (see *raw_getpathmo* in *lib/fog/vsphere/requests/compute/list_datacenters.rb*).

Let me know what you think.

Thanks Marc.